Heat exchanger



Mav 7, 1940. P. R. cAss|Y HEAT EXCHAGER Uriginal Filed Aug. 5. 1935 A 'Sheets-Sheet 1 Perry R. Cassidy May 7,V 1940. P. R. cAsslDY 'HEAT xaxcmfmcnm' original Filed Aug'. 3. 1935 2,2oog156 4 slums-sheet. 2

INVENTOR. Perry l?. Cassidy BY E R ATTORNEY'.

P. R. cAssmY 2,200,156

mm sxcmesn original ingang. s, 1935 4 shuts-sunt 5 INVENTOR.; pez-zy Cassidy ATTORNEY.

Ml? 7, 1940. P. R. cAssmY nur''xaxcmmman` Original Filed Aug. 3. 1955 4- shuts-Shout 4 oom. o..o o

INVENTOR, Perry R Cassidy ATTOY.

Patented May 7, 1940 naar Examens Perry B.. Cassidy,'Short,Hills, N. J., aligner to The Babcock & Wilcox Company, Newark, vN. J., a corporation of New Jersey Application August s, 1935, serial No. 34.506 Renewed 'A pril 1K5, 1937 'UNITED STATES.-

22 claims.

My present invention relates in general to the construction and operation of heat exchangers, and more particularly, to heat exchangers' especially adapted for the recovery of heat from corrosive, or potentially corrosive, gases, while under a pressure above atmospheric. y

The main object of my invention is the provision of a tubular heat exchanger of thecharacter specified which is further characterized by a higher operating efficiency, greater heat absorbing capacity per foot of space occupied, less maintenance cost, and greater ease of access for curs due to condensation of water vapor in the Y heating gases on the tubes and itsy combination with the corrosive constituent or constituents of the gases.

In accordance with my invention an unusuallyv high operating eiciency is maintained in such heat exchangers by the provision of a gas-tight casing for the gases, reduction of external heat losses, eiective arrangement of the heat absorbing surface, low pressure drop through the apparatus, and low cost of maintenance of the apparatus. A particularly low cost of maintenance is possible as all of the tube joints are located in zones free from corrosive gases so that any leakage occurring at the joints is of minor consequence, the joints may be conveniently examined without interrupting the operation, the tubes may be cleaned throughoutl their length with a standard turbine cleaner, and tube repairs andreplacements may be readily eiected by removing Van entire section oi' the heating surthe heating surface to facilitate starting of the associated fuel burning apparatus and to maintain the outlet temperature of the heating gases from the heat exchanger above the condensationy point of the water vapor included therein.

The various features of novelty which characterize my invention arey pointed out with particularity in the claims annexed to and forming 5, a part of this specication. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference shouldv be had to the accompanying drawings and descriptivematter in which I have ill0 lustrated and described a preferred embodiment of my'invention. l

My invention is specically illustrated as embodied in a steam generating unit for cooling and recovering heat from corrosive gases under pressure and mainly consisting of sulphur dioxide; and in the drawings:

Fig. 1 is a longitudinal'vertical section-taken onthe line I-I of Fig. 2;

Fig. 2 is a transverse vertical 'section taken on the line 2-2oi Fig. 1;

Fig. 3 is 'a front view of the unit;

Fig. 4 is a horizontal section taken on the line 'L -4 of Fig. 2;

Fig. 5 is a horizontal section taken on theline 25 5-`5 of Fig. `il; D

Figs. 6'and 7 are side and transverse sectional views respectively of the tube supporting arrangement; v

f Fig. 8 is a transverse vertical section taken on the line 8 8 of Fig. 1;

Fig. 9 is a horizontal section taken on the line 9-9 of F18. 8; Fig. 10 is a horizontal section taken on the line lli-I0 of Fig. 8; 35 Fig. 11 is an enlarged View of one of the walls shown in Fig. 1;

. Fig. 12 yis a vertical section taken-on the inner side of the wall illustrated in Fig. 11;

Fig. 13 is a horizontal section taken on the line Iii-I3 of Fig. 1;

Fig. 14 is a vertical section taken on the line M M of Fig. 13; and l Fig. 15 an enlarged view of a portion of Fig. y5.

In the embodiment oftheinvention illustrated in the drawings a gas-tight casing is formed by, a vertical front wall l, a rear wall 2, opposite side walls 3 and 4, a iioor5, and arched roof 6,- collectively defining va casinggsubstantially rectangular in horizontal and vertical cross-section. The side wall 3 is'provided adjacent its lower end with a corrosive gas inlet 1, while the opposite side wall- 4 has a gas outlet 8 of smaller diameter than and concentric with the gas inlet 1. The interior of the casing is divided into a .tubes may be ofA corrodible steel. -header boxes I4 are arranged externally of the gaspasses forserially connecting the adjacent palr-oftverncal upnow and Ydowntow,serially/J connected gas passes 9 and I0 respectively by a@ y y `,"nection 29 opensto each .compartment and the longitudinally extending iire brick baille II extending/upwardly from vthe floor 5 and terminating shorty of the roof 5. By this` arrangemenirthe, hot gases entering the inlet I will pass upwardly E Ithrough the gas pass- 9, over the upper end of the baille II, downwardly throughthe gas pass I9, and exit through the gas outlet 3. 'Ihe heat absorbing surface of the unit coniprises a vertical series of horizontal rows /ofsin'- gle return bend or U-tubes I2 and I3 extending longitudinally of eachof the-Jgas passes from opposite end walls of the casing. 'I'he tubes I2 have oppositely inclined vertically alignedleg portions extending through the front' wall I, while the tubes I3 have oppositely inclinedleg portions extending through the rear wall 2. As shown in Figs. l and 2, each of the tubes I2 has its leg .portions arranged substantiallyA parallel to and staggered relative to the correspondingly inclined leg portions of 'thetubes' I3 in the vertically adjacent rows', and its return bend or loop portion adjacent to the opposite side ofthe gas\pass and extending transversely of the adjacent leg portions of ycorresponding tubes l I 3 in vertically adjacent rows, and vice versa. Three U-tubes VI2 or I3 :are shown in each horizontal -row so that,l as shown in Fig. -2, there will be vertically spaced groups of six staggered tube legs in each gas pass of the heat recovery zone. The Groups of leg portions of corresponding tubes I2 in vertically adjacent rows. Corresponding header boxes I5 serially connect corresponding tubes I3 'in a similar manner. Two sets of parallel iiow fluid circuits are thus provided foreach gas pass with all connecting joints external thereof.

When the tubesl I2 and I3 constitute the heat absorbing surface of a steam boiler, a steam and water drum I6 is symmetrically arranged longi legs of the tubes I3 in qne gas pass.

tudinally of and supported on the 'roof of the casing. A positive uid circulation is maintained between the drum I5 and the tubes I2 and I3 by means of pairs of downcomer tubes I1 and I9 respectively extending from the bottom of. thedrum I6 to pairs of headers I9 and 29 respectively. Each header I9 is connected to the lowermo'st legs of the tubes I2 in one gas pass, while each header 20 is connected to the llo'wermostl The uppermost legs of the tubes I2 are connected to separate header boxes 2| having separate detach-- ably connected -risers '22 leading to the drum I6.

.The uppermost legs of the tubes I3 are similarly connected through boxes23 and'risers 24 toy the drum I6. The header boxes I4, I5, 2|, and 23, and headers I 9 and 20 are provided-with the usual hand hole connections for expandingand cleaning the tubes connected thereto. The drum I3 is provided with the usual steam outlet, gage, and safety "valve connections. VThe described` location of the drum I6 provides a relatively high head and with the inclination oi'. the tube 'legs insures a rapid fluid circulation through all parts of the heat absorbing surface, thus minimizing overheating andl burning out oi' the tubes VI2 The drum I6 is provided with a pair of spaced internal bai'lles 26,'one at each end of the drum, extending longitudinally of and across the bottom of the drum. The baiiies are closed at one en`d by plates 23 to provide a pair of similar'comvallergico culationfthrough the I oi connection is provi edfor the headers I9 and l0 ppt-i i j partments''l' openv at their` ends adjacent Lthe middle ofdzhewdrum. A jfe'dwater supply conlowncomers vIl and I3 also open into the conl- "partments adjacent their closed ends. Y The risers 5 22 and 24 fhowever, are connected to the drum.l I5 above/ the compartments. This internal drum construction aids in maintaining a positive cir-I t bes,I2 and I3. A blow-- 20 .and comprises angle valvesw29, pipe 30, a T :Ipanfivlye a2, at each end of the unit, as shown in Figs. land 3. f

'I'he specic construction of. the casing will now vbe described;v Each of the side walls 3 and l5 4 is'fornied by a welded sectional metallic cover f 33 'to which'is welded spaced rows of Ts 34 for anchoring a thick wall of I insulating fire brick Q35 in position. A layer fof mill'board 36 is provided between the refractory 'and metallic cover, 20 as shown in Figs. 13 and lli-. l

The construction of the front` and rear walls is specifically illustrated -in Figs. l, 3, and 8-15. Each of these walls has a lower section 40 below the tubes I2 and I3 constructed similarly to the 25 side wall construction shown in Figs. 13 and 14, and an upper section 4I of less thickness forming avv gas-tight closure for the front and rear sides of the gas passesfand having an outer casing 42 for enclosing the pressurel parts externally of the 30 gas-passes. Each upper wall section 4I has 'a steel framework l43 fitting around the front and rear sides of the corresponding gas passes and in gas-tight contact with the ends of the 'side walls 3 and 4 and'baflie II, (see Fig. 15) and re- 3 movable panels 44 fitting into and closing the corresponding sides of the 'gas passes. As shown,V each panel. 44 consists o1. ametallic tube sheet 45' which is detachably connected to the framework by clamps 45 and covered at its inner side by 4.0

mill board 41. The tube sheet carries spaced sections of insulating brick 43 between the areas through which the tubes project. The tubes are supported on the panel by having their leg portions expanded into the tube sheetv and lling 45 the vsections between the brick 48 with plastic refractory 49. The construction described provides a gas-tight enclosure capable of withstanding gas pressures up to l0 lb. per sq. in. without leakage, while minimizing external heat losses. The location of all of the tube joints in an area. free from the heating gases avoids corrosion at these points which would otherwise occur due to presence of moisture from small leaks and sweating at the tube joints, which ordinarily combine 55 with the gases and cause local corrosion.

The outer paneled casing 42 which extends over each wall portion 4I is made up by a metallic framework 50 (Fig. 3). which extends outwardly beyondthe pressure parts and has its front closed .60 by upper and lower panel sections 5I and 52v re. spectively, as shown in Figs. 1 and 3,-normally held in position by clamps 53 and removable to permit inspection, cleaningand replacement of .the tubes. By this arrangement all of the tubes w05 I2 or I3 in one gas pass can be removed as a unit by simply removing the panels 5I and52, disconnecting the riser and downcomer connections, and unbolting the clamps 46 holding the.- corresponding tube sheet in position. f. u 70 The panels 44 thus provide a cantilever support for the corresponding tubesv I2 and I3. Thel inclination of the tube legs also strengthens the U-tubes. Each of the tubes is thus free to expand and contract at' its return bend end duringl ascenso,

operation. rAsshcrwn in Figs.; 1, 8, 7, and 15,'the looped ends of the tubes I 2 are prevented from sagging and the tubes held in their desired positions relative to the adjacent tubes by welding va. study 60 to the side of each loop portion'in throughy the narrow gasv passes and I0' across the tubes I2 and I3 therein. which being closely spaced provide a high heat transfer rate by convection. AThe relatively wide spacing of thetube leg groups permits thick gas layers between Ithe groups anda high rate of h eat.transfer `by gas radiation. 4While the pressure drop through the unitis relatively low due to the presence of only one baiiie t l1 erein, it may be desirable under certain circumstances, suchias to facilitate starting oftheunit or particularly, to regulate the passage i'. the gases. through the unit so thatthegas out.- let temperature willbe suflic'iently high to prevent condensation of moisture in `the gases and consequent. formation of corrosive acids, rto bypass allor. a portion offthe gases around the heat recoveryzone. f l Forthis purpose controllable bypass openings 65 are providedthrough the baie f I I 'belowthe heating surface topermit the lgases to'sli'ort-circuit the heatingj surface, as shown in Figs.1 Zande. 'I'he yrectangular openings are 'spaced along'the bottom ofthe banlef I I and each isprcvide'd ,with a' dampenme es ,atitsouuet sidey and mechanism for movingthe title toopen and close the by-pass opening. The. lower end of each damper tile is rounded and nts vinto, a

recessed block 61 in the bottom of the downflow passage I0.. Pairs of blocks 6 8 along the bottom of lthe sidewall 4 serve as supports l for each damper -tile in its .tilted position. The mechanismvfor independently operating each damper tile consists of links 10 and 1I .respectively connectedvto the damper tile and to an operating shaft 12 journaled in a gas-tight housing 13 below the level of the gas outlet 8. The shaft 12 is actuated by a hand lever 14 as indicated. By

-these means the amount of gas passing through the heat recovery'zone may be controlled to maintain the gas outlet temperature above the ycondensation temperature of vthe contained water vapor.

While in accordance with the provisions'of the statutes I have illustrated and described herein the best form of my invention now known to me, those skilled in the art will understand that changes maybe made in the formv of the apparatus and method of operation disclosed without departing from the spirit of the invention covered by my claims, andthat certain features of my invention may sometimes be used to advantage without a corresponding use of other features. In the specification and claims the word corrosive" is intended to generically cover both corrosive gas per se and potentially corrosive gases which form corrosive compounds when combined with liquids.

I claim:

1. A heat exchanger -comprising a casing compricing return bend tubes extending horizontally in said casing from opposite' ends thereof, each of said tubes having a return bend portion extending transversely of vertically adjacent leg yp ortions of vertically adjacent tubes extending from the opposite end of the casing, and means providing a support for said return bend .portion from one of said transversely extending leg portions.

2. A heat exchanger comprising a casing infcluding return bend'tubes extending horizontally in said casing and cantilever supported from opposite ends thereof, each of said tubes having a return bend portion extending transversely'ofA horizontally extending oppositely inclined leg portions of vertically adjacent tubes supported at the opposite end of the casing,I and means providing a support for each of said return bend portions from one of said adjacent legportions.

3. A heat exchanger comprising a casing including vertically spaced rows of single return bend tubes, said `tubes extending horizontally in said casing and being cantilever supported from opposite ends thereof, each of said tubes having a return bend portion extending transversely of laterally adjacent leg portions of tubes supported at the oppositej'end of the casing, and means)y providing a support for each 'of s aid return: bend portions from one of said laterally adjacent legv portions.

4. A heat exchanger comprising a casing, heat transfer surface v comprising horizontal rows of return bend tubes, said tubes extendingin vertical planes transversely of said casing from opposite ends thereof, and Veach ofsaid tubes having a return bend portion extendingtransverselyof and across the adjacent leg portions of verti-v cally adjacent tubes in superposed rows extending from the opposite end of the casing.

'5. A heatvexchanger comprising a casing, heat transfer'surface comprising verticaly spaced horiextending in vertical planes transversely of said casing from opposite ends thereof, each of said tubes having oppositely inclined leg portions extending between and staggered relative to the leg portions of adjacent return bend tubes extending from the opposite end of said casing, and each of said tubes having its return bend portion adja-y cent to said opposite rend of the casing and extending transversely of the adjacent leg portions of vertically adjacent tubes in rows extending from the opposite end of the casing,

6. A heat exchanger comprising a casing, heat transfer surface comprising horizontal rows of return bend tubes, said tubes extending transversely ofv'said casing from opposite ends thereof, said casing having a tube sheet at each end thereof, each of said tubes having leg portions extending through and expanded into the corresponding tube sheet and arranged in a plane between the planes of return bend tubes extendingthrough the ltube sheet at the opposite end of said casing, and headers externally of said tube sheets and connecting the ends of tube legs of adjacent tubes supported by the same tube sheet.

'7. A fluid heater comprising a casing,v heat absorbing surface comprising horizontal rows of single return bend tubes, said tubes extending transversely .of said gas pass and cantilever supported from opposite sides thereof, each of said tubes having a pair of oppositely inclined leg portions arranged in a plane between the planes of laterally adjacent return bend tubes supported from the opposite side of said gas pass, a liquid and vapor drum, downcomer tubes providing a 40 zontal rows of single return bend tubes, said tubes l' 4 liquidsupply from said drum to thelowerinost tube legs, means connecting corresponding tubes in said rows supportedl at the same side of said gas pass for a serial uid ilow therethrough, and riser tubes connecting. the uppermost tube,A legs to said drum. f

8. A fluid heater comprising a casing, heat absorbing surface comprising vertically spaced horizontal rows of single return bendv tubes, said tubes extending transversely of said gas pass from opposite sides thereof, said casing having a remov- .able metallic tube sheet at each side of vsaid gas pass, each of said tubes having leg portions extending through and Aexpanded into the corresponding tube sheet and `arranged between the leg portions of laterally adjacent return bend tubes extending through the tube sheet at the oppositey side of said gas pass, headers positioned externally of each tube sheet and serially connecting adjacent leg portions of vertically adjacent tubes, a liquid and vapor drum, downcomer tubes providing aliquid supply from said drum to the lowermost tube legs, and riser` tubes connecting the uppermost tube legs to said drum.

9. A heat exchanger comprising a casing, heat transfer surface comprising horizontal'. rows of return bend tubes, said tubes extending trans-1 versely of said casing from opposite ends thereof.

each of said tubes having a return bend portion extending transversely of the laterally adjacent leg portion of a :tube Supported `at the opposite end of the casing, and means providing asupporting connection between the return'bend pory tion of said tube portion. l v l 10. Aheat exchanger comgising a casing, heat transfer surface comprising horizontal rows of return bend tubes, vsaidtubes extending transand said laterally adjacent leg versely of said -casing'from opposite ends thereof,

each of said tubes having leg portions extending between the leg portions of .adjacent return'bend tubes extending from the ,opposite end ot-said casing, each of said tubes having a return bend portion adjacent to said` opposite end of the casing and extending transversely of the adjacent leg portions of vertically adjacent tubes in rows 1 extending from the' opposite end. of the casing,

and means providing a supporting' connection between the return bend end of said tubes and one of said laterally adjacent leg vportions permitting relative expansionnd contraction of said tubes.

1l. A heat exchanger comprising a casing,

heat transfer surface comprising horizontal rows of return bend tubes, said tubes extending transversely of said casing from opposite ends thereof, said casing having a removable metallic tube sheet at each end thereof, each of said tubes hav' ing leg portions extending through andexpanded into the corresponding tube sheet and arranged in a plane between the planes cf laterally adjacent return bend tubes extending through the tube sheet at the opposite end of said casing, each 12. A heat exchanger. comprising heat transfer surface including vertically spaced horizontal rows of single return bend tubes, a casing for said 2,906,150 v siufaceincluding a 'tube supporting plate, eachr of said tubes having a pair of oppositely inclined l leg portions' extending through and expanded into said supporting plate to form a cantilever support for said tube, and headers arranged externally of said supporting plate for serially connecting y and being supported on the projecting/ends of adjacent leg portions of vertically adjacent tubes.

13. A heat exchanger comprising a casing, heat transfer surface comprising vertically spaced horizontal rows of single return bend tubes, said tubes extending transversely of said caslngfrom opposite ends thereof, said casing having a removable metallic tube sheet vat each end thereof, eachfof said-tubes having oppositely inclined leg portions extending through and expanded into the corresponding tube sheet and arranged between and staggered relative to the leg portions turn bend portion adjacent to said opposite end y of thecasing and extending'transversely of the adjacent leg portions of vertically adjacent tubes in rows supported at said opposite end of the casing, vand means vproviding a supporting' connection for the return bend end of said tubes including a stud extending from each return-bend portion and supported on one of said laterally adjacent leg portions.

14.l A iiuid heater comprising a casing, heat absorbing surface in said casing comprising vertically spaced horizontal rows ci return .bend tubes, said tubes extending'ltransversely of said casingv from opposite ends'thereof, said casingl having a removable metallic tube sheet at each endthereoff, e'ach of said .tubes having leg por- 4 v tions extending through and expanded intfo the corresponding tube sheet'and arranged between the leg portions oi' laterally adjacent return bend tubes extending through the tube sheet at'the opposite end of said casing, headers positioned externally of each tubesheet and serially connecting adjacent leg. portions of vertically adjacent tubes, a liquid and vapor drum. downcomertubes providing a liquid supply from said e ldrum to the lowermost tube legs at each end of' said casing, and riser tubes connecting thev uppermost tube legs at each end of said casing yto said v15J; fluid heater comprising a casing having a gas inlet and a gas outlet at opposite sides thereof, a baille arranged tcv divide said casing i into a pair of upfiow and downilow gas passes communicating at their lower kends with said gas inlet and outlet respectively, heat absorbing surface comprising horizontal rows of return bend tubes, said tubes extending transversely of each of said gas passes from opposite sides thereof, each of said tubes having'leg portions arranged in a plane between the planes of laterally adjacent returnbend tubes extending fromy the opposite side of said gas pass, each of said tubes having its return bend portion adjacent to one of said opposite sides of the gas Vpass and extending transversely of the adjacent leg portions of verti; cally adjacent tubes in rows extending from the other of said opposite sides of the gas pass, and

lheaders serially connecting adjacent leg portions of vertically adjacent tubes.

16. A iluid heater comprising a casing having a gas inlet and a gasl outlet at Opposite sides thereof. a baille arranged to divide said'caslng into a pair of upow and .downflow gas passes communicating at their lower ends with said gas aaoonse inlet and outlet respectively, heat absorbing surface comprising vertically spaced horizontal rows of single return bend tubes, said tubes extending transversely of each of said gas passes from opposite sides thereof, said casing having a removable metallic tube sheet at said opposite sides oi' said gas passes, each of said tubes having inclined legportions extending through and expanded into the corresponding tube sheet and arranged between and staggered relative to the leg portions of laterally adjacent return bend tubes extending through the tube sheet at 'the opposite side of said gas pass, each of said tubes having its return bend portion adjacent; to one of said opposite sides of the gas pass and extending transversely of the adjacent leg portions of vertically adjacent tubes in rows supported atthe other of said opposite sides of thegas pass, headers positioned externally of each tube sheet and serially connecting adjacent leg portions of vertically adjacent tubes, a liquid and vapor drum, downcomer tubes providing a. liquid sup-y ply from said drum to the lowermost tube legs, and riser tubes connecting the uppermost tube legs to said drum. f

17. A heat exchanger comprising heat transfer surface including a plurality of return bend tubes, a casing for said surface including a tube supporting plate, each of said tubes having a pair of leg portions extending through and expanded into said supporting plate to form a cantilever support for said tube, and a header separate from and arranged externally kof said supporting plate for serially connecting the projecting ends of leg portions of different tubes.

18. A heat exchanger comprising heat transfer surface including a plurality of single return bend tubes, a casing for said surface including a tube supporting plate, each of said tubes having a pair of oppositelyinclined leg portions extending through and expanded into said supporting plate to form a cantilever support for said tube,

-and a header separate from and arranged externally of said supporting plate for serially con- .necting the projecting ends of adjacent leg portions of adjacent tubes.

19.l A fluid heater comprising a casing having vertically spaced rows of return bend tubes, said tubes extending horizontally in said casing andbeing cantilever supported from opposite ends thereof, means connecting corresponding tubes in said rows supported at the same end of said casthe opposite en d :the casing.

ing for a serial uid ow therethrough, a liquid and vapor drum, conduit means providing-a liquid supply froml said drum to the lower ends of said serially connected tubes, and other conduit means connecting the upper ends of said serially connected tubes to said'drum.

20. A fluidv heater comprising a casing having a gas inlet and a gas outlet, baiiie means forming a` plurality of gas passes between said gas inlet and outlet. heat absorbing surface comprising vertically spaced rows of return bend tubes, said tubes extending horizontally in each of Ysaid gas passes and being cantilever supported from opposite sides thereof, each of said tubes having a return bend portion adjacent to one lof. said opposite sides of the corresponding gas pass and extending transversely of one of the leg portions of a tube supported at the other of said opposite sides o'f said gas pass, means connecting corresponding tubes in'said rows supported at the same side of each gas pass for a serial fluid flowtherethrough, a liquid and vapor drum, conduit means providing a separate liquid supply from said drum vto the lower ends of the tubes supported at each side of said gas passes, and other conduit means connecting the upper ends of said tubes to said drum. l

21. A heat exchanger comprising heat transfer surface including a plurality of return bend tubes, a casing for said surface. including a tube supporting plate, each of said tubes having a pair of leg portions extending through and expanded into said supporting plate to form `a cantilever support for said tube, and a header arranged externally of said supporting plate for serially connecting and being supported. on the projecting ends of leg portions of different tubes. 22. A heat exchanger comprising a casing, heat transfer surface comprising horizontal rows of return bendtubes, said tubes extending in vertical planes transversely of said casing from opposite ends thereof, each of said tubes having leg portions extending between and staggered relav the adjacent leg portions of vertically adjacent,

serially oonnectedtubes in rows extending from PmRY R. CABSID'Y.v 

